Constance Casey's profiles of revolting creatures.

Revolting Creatures

A series of unlovely profiles.

In the summer of 2008, Slate's Constance Casey began an open-ended mission to profile—and perhaps rehabilitate—the most disgusting animals you're ever likely to meet. By exploring the life stories of these nasty critters, she explains how they fit into the world around us. So why did God create ticks? What's the point of a jellyfish? Excerpts from each column are printed below, along with links to the full text.

The TickTicks not only extract blood, they ooze pathogens from their salivary glands into the wound they've sliced with their tiny claws and penetrated with their barbed mouthparts. …

I managed to locate Willy Burgdorfer, the scientist who identified the Lyme spirochete in 1982, and asked, "Why did God make ticks?"

"I don't have the answer," Dr. Burgdorfer said. "There are a lot of things we assign to the good Lord and we ask the question, why? All I can advise is to check yourself for ticks and remove them fast."

The JellyfishA profusion of jellyfish is often described as an invasion or an attack. Which is laughable, given the guiding principle of jellyfish behavior—"whatever." No brain, no spine; they don't have the capacity to plan a beach invasion. We bump into them, and because we're too big to eat, they perceive us as attackers.

Planning is not their forte. In place of a brain, jellies have a nerve net. Jellyfish are the free-floating relatives of sea anemones and corals, much older than fish, and not much changed for more than 600 million years. They ruled the ocean, in their passive way, when there was almost nothing but ocean. Now they drift into their food or their food drifts into them. The pulsing creates a current that pulls prey within reach.

The VultureUnder threatening circumstances, an angry bird can aim green vomit at you from as far away as six feet. Normally, though, a turkey vulture's sociability extends to human beings as well as to its fellows. The people who care for injured wild birds report that vultures are gentle, inquisitive, and smarter than hawks and eagles. Here's the bottom line, according to one expert: "Once they get to know you they don't regurgitate on you."

The SlugIn most kinds of slug, the penis is about half the length of its body. ("Is that a Kalashnikov in your pocket or are you just glad to see me?") It's not clear why such anatomical grandeur might be important for survival: Slug experts discount the idea that the oversize penis functions like a peacock tail, as a display of virility—they point out that the chemical signaling and seduction occurs before the magisterial organs even come into view. In any event, the chosen mate isn't likely to be impressed, since most slugs possess both male and female sexual organs. During a single coupling, slugs can mate reciprocally—with each partner inseminating and being inseminated—or one can serve as the recipient.

The Snapping TurtleThey're shy but not beautiful, these creatures of the mud, and I have seen them up close. A couple of summers ago, I was swimming in my upstate New York pond and saw, a few yards away on the surface of the water, a curious combination of moving body parts. There was a glossy, ridged back, then another glossy back, a scaly paw with bearlike claws, and part of a thick, thorny tail.